linux-kernel - Re: [PATCH 0/10] Add additional security checks when module loading is restricted

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Date:	Wed, 28 Aug 2013 16:07:06 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Lenny Szubowicz <lszubowi@...hat.com>
Cc:	Matthew Garrett <matthew.garrett@...ula.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Josh Boyer <jwboyer@...hat.com>
Subject: Re: [PATCH 0/10] Add additional security checks when module loading
 is restricted

On Wed, Aug 28, 2013 at 3:58 PM, Lenny Szubowicz <lszubowi@...hat.com> wrote:
>
>
> ----- Original Message -----
>> From: "Matthew Garrett" <matthew.garrett@...ula.com>
>> To: "Lenny Szubowicz" <lszubowi@...hat.com>
>> Cc: linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org, jwboyer@...hat.com, keescook@...omium.org
>> Sent: Wednesday, August 28, 2013 6:41:55 PM
>> Subject: Re: [PATCH 0/10] Add additional security checks when module loading is restricted
>>
>> On Wed, 2013-08-28 at 18:37 -0400, Lenny Szubowicz wrote:
>>
>> > Did you purposely exclude similar checks for hibernate that were covered
>> > by earlier versions of your patch set?
>>
>> Yes, I think it's worth tying it in with the encrypted hibernation
>> support. The local attack is significantly harder in the hibernation
>> case - in the face of unknown hardware it basically involves a
>> pre-generated memory image corresponding to your system or the ability
>> to force a reboot into an untrusted environment. I think it's probably
>> more workable to just add a configuration option for forcing encrypted
>> hibernation when secure boot is in use.
>>
>> --
>> Matthew Garrett <matthew.garrett@...ula.com>
>
> I'm root. So I can write anything I want to the swap file that looks
> like a valid hibernate image but is code of my choosing. I can read
> anything I need from /dev/mem or /dev/kmem to help me do that.
> I can then immediately initiate a reboot.

Strictly speaking, RAM contents are not available via /dev/*mem, even
to root. However, you can request a suspend image be written, but to
not enter hibernation. Then modify the image, and request a resume
from it.

-Kees

-- 
Kees Cook
Chrome OS Security
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